Highly hard material coated articles

ABSTRACT

This invention relates to a highly hard material coated article which comprises a substrate of tool or part consisting of cermets, cemented carbides, tool steels or stainless steels and at least one highly hard material coated on the surface thereof, selected from the group consisting of carbides, nitrides and carbonitrides of at least one of titanium, zirconium and hafnium and those in which oxygen is dissolved, the coating being formed by an ion plating method wherein the accelerating voltage is high in a short time at the initial stage only, the crystals of the coated film being strongly orientated in the direction of &lt;220&gt; for the surface of the tool or part so that the diffraction intensity ratio of the peak from the {220} plane and the secondly strong diffraction peak in the X-ray diffraction using Cu-Kα ray, that is, the diffraction intensity ratio is 15 or less of the latter to 100 of the former and the half value width of the diffraction peak from the {220} plane of the coating film being 0.8° or more than 2 θ scale.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to novel highly hard material coated articles andmore particularly, it is concerned with highly hard articles, forexample, cutting tools such as turning tools and cutters, wear resistingtools such as metallic molds and wire drawing dies, wear parts such asbearings and cams, and decorations such as watch frames, coated for thepurpose of raising the wear resistance, heat resistance and corrosionresistance with high hardness, high melting point and high chemicalstability compounds such as carbides, nitrides, or carbonitrides oftitanium, zirconium, hafnium or their alloys, or those in which oxygenis dissolved, with a thickness of 1 to 20 microns.

2. Description of the Prior Art

It is well known to coat a tool or part with titanium carbide ortitanium nitride in order to improve the wear resistance, heatresistance and corrosion resistance thereof and this is put to practicaluse. For the fabrication of the coated article, the chemical vapordeposition method (CVD method) or dipping-in-fused salt methodrepresented by "TD process" is used, but these methods are all coatingmethods carried out at high temperatures such as about 1000° C., sothermal deformations or structure changes tend to occur in thesubstrates of tools or parts although the adhesion strength between thecoating film and substrate is considerably large due to diffusion. Thus,their use is considerably limited. For example, if the substrate is of atool steel, it is annealed and if stainless steel, the corrosionresistance is deteriorated. The substrate of a cemented carbide alloytends to be brittle.

On the other hand, progress of the physical vapor deposition method (PVDmethod) is remarkable and titanium carbide or titanium nitride can becoated even at low temperatures such as below 500° C. The so-calledphysical vapor deposition method includes the vapor deposition method,sputtering method, activated reactive vapor deposition method (AREmethod), hollow cathode discharge vapor deposition method (HCD method),ion plating method and the like, but above all, the ion plating methodwherein a material to be vapor deposited is much energized as positiveion by applying a negative accelerating voltage to a substrate is mostpreferable for increasing the adhesion strength between the coating filmand substrate. This ion plating method can be classified into two kindsof the high pressure type (low vacuum type) in which ionization iscarried out by glow discharge in an ambient gas under a pressure of 0.5to 3 Pa, and the low pressure type (high vacuum type) in whichionization is carried out by an intermediate electrode, electronirradiation or high frequency electric field under a pressure of 0.1 Paor less. However, the ion plating method of the high pressure type hasthe disadvantage that because of its high ambient pressure, the coatingfilm of titanium carbide or titanium nitride tends to be weak and nosufficient adhesion strength is obtained since the acceleration of ionsis carried out mainly at the cathode dark portion about the basematerial. In the case of the low pressure type, on the other hand, acoating film of good quality can readily be obtained and it is possibleto accelerate sufficiently ions with a substantially uniform potentialgradient, resulting in a high adhesion strength, but the film qualityand adhesion strength are largely affected by the ionization efficiencyand accelerating voltage. The ordinary ion plating method is not soeffective for increasing the adhesion strength because the ionizationefficiency is generally low and the energy given to a material to bevapor deposited cannot be increased so much even if the acceleratingvoltage is increased. Consequently, there have been proposed the HCDmethod and ARE method whereby the adhesion strength is increased byheating a substrate without applying an accelerating voltage, but theadhesion strength is not sufficient at low temperatures and theadvantages of the physical vapor deposition method as described aboveare lost at high temperatures. When applying an accelerating voltageusing the ordinary ion plating apparatus with a low ionizationefficiency, for example, the current flowing through an acceleratingelectrode (in general, substrate) is very small, i.e. about 0.01 to 0.2A even if the accelerating voltage is considerably high.

The inventors have hitherto employed such an ion plating process in astudy on the coating of cemented carbide inserts with a layer of TiN orTiC for comparison with the chemical vapor deposition process, asdisclosed in "Thin Solid Films" 54 (1978) p 67-74. According to thisstudy, it is apparent that the wear resistance of carbides coated by ionplating is similar to that of carbides coated by chemical vapordeposition, but the toughness obtained by ion plating is superior tothat of chemically vapor deposited coatings. In addition, the inventorshave also proposed a coated tool steel comprising a tool steel substrateand a coated film thereon consisting of at least one of titanium,zirconium and hafnium carbides, nitrides and carbonitrides, which has agreater half value width, as disclosed in U.S. Pat. No. 4,169,913.However, these coated articles are not satisfactory in adhesion strengthbetween the substrate and coating.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a highly hardmaterial coated article excellent in wear resistance, heat resistanceand corrosion resistance.

It is another object of the present invention to provide cutting tools,wear resisting tools, wear parts and decoration articles with animproved wear resistance, heat resistance and corrosion resistance.

It is a further object of the present invention to provide a coatedarticle with an improved adhesion strength between the substrate andcoating by ion plating method.

These objects can be attained by a highly hard material coated articlewhich comprises a substrate of tool or part consisting of cermets,cemented carbides, tool steels or stainless steels and at least onehighly hard material coated on the surface thereof, selected from thegroup consisting of carbides, nitrides and carbonitrides of at least oneof titanium, zirconium and hafnium and solid solutions thereof and thosein which oxygen is dissolved, the coating being formed by an ion platingmethod wherein the accelerating voltage is high in a short time at theinitial stage only, the crystals of the coated film being stronglyorientated in the direction of <220> for the surface of the tool or partso that the diffraction intensity ratio of the peak from the {220} planeand the secondly strong diffraction peak in the X-ray diffraction usingCu-Kα ray, that is, the diffraction intensity ratio is 15 or less of thelatter to 100 of the former, and the half value width of the diffractionpeak from the {220} plane of the coating film being 0.8° or more on 2θscale.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing is a schematic view of an ion plating systemused in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The inventors have made various efforts to overcome the disadvantages ofthe prior art, in particular, to improve the ion plating method andapparatus therefor and consequently, have found that a highly hardmaterial coated article excellent in adhesion strength between thesubstrate and coating can be obtained under the specified conditions inthe ion plating method.

In the high hard material coated article according to the presentinvention, the surface of a tool or part is coated with at least onehighly hard material selected from carbides, nitrides and carbonitridesof titanium, zirconium, hafnium and solid solutions thereof and thosecompounds in which oxygen is dissolved, and the crystals of the coatedfilm are strongly orientated in the direction of <220> for the surfaceof the tool or part so that the diffraction intensity ratio of the peakfrom the {220} plane and the secondly strong diffraction peak in theX-ray diffraction using Cu-Kα ray, that is, the diffraction intensityratio is 15 or less of the latter to 100 of the former.

In an ion plating apparatus used in the present invention, theionization efficiency is high and the electric current passing throughan accelerating electrode is extraordinarily great, i.e. at least 1 to20 A even if the accelerating voltage is low. Because of such a highionization efficiency, the energy of the individual ion of a material tobe vapor deposited can be increased by raising the accelerating voltage,thus resulting in a coating film with a high adhesion strength. Thecrystals of the coating film obtained in this way are stronglyorientated in the direction of <220> for the surface of the substrate.According to the results of our studies, it is found that the adhesionstrength is sufficiently great on practical use when the diffractionintensity ratio of the diffraction peak from the {220} plane and thesecondly strong diffraction peak in the X-ray diffraction using Cu-Kαray, that is, the diffraction intensity ratio is at most 15 of thelatter to 100 of the former. In this range, for example, the coated toolcan be used in interrupted turning operations. When this ratio is lessthan 10, the coated tool has a high adhesion strength and has a goodperformance in milling operation in which the prior art coated toolcannot favourably be used.

In the present invention, however, the electric current passing througha substrate is great, i.e. 1 to 20 A, so if the accelerating voltage isfor example 1.5 KV, the electric power applied to the substrate is 1.5to 30 KW and the temperature of the substrate is markedly increased.Thus, there is a possibility of deteriorating the feature of thephysical vapor deposition method that coating can be accomplished at alow temperature.

Furthermore, it is also found by our studies that when coating iscarried out using an ion plating apparatus with a high ionizationefficiency, the crystalline disorder of the coating film is increasedwith lowering of the temperature and the half value width of thediffraction peak in the X-ray diffraction is great. Herein, it is to benoted that the greater the half value width, the more improved the wearresistance of the coating film. For example, when the half value widthof the diffraction peak from the {220} plane of the coating film inX-ray diffraction using Cu-Kα ray is at least 0.8° on 2θ scale, there isgiven a very excellent wear resistance, and when at least 1°, the wearresistance is more improved.

That is to say, if in the X-ray diffraction using Cu-Kα ray, thediffraction intensity ratio of the peak from the {220} plane and thesecondly strong diffraction peak is at most 15 of the latter to 100 ofthe former, and the half value width of the diffraction peak from the{220} plane is at least 0.8° on 2θ scale, there can be obtained a coatedarticle having an excellent adhesion strength of the coating as well asa high wear resistance.

However, in order to lower the diffraction intensity ratio to 15 orless, it is necessary to raise the accelerating voltage applied to asubstrate while in order to increase the half value width, it isnecessary to lower the accelerating voltage.

The inventors have made efforts to solve this contradictory problem andconsequently, it is found that the diffraction intensity ratio isdetermined by the voltage at the initial period of coating and the halfvalue width depends upon the electric power. Based on this finding, theaccelerating voltage at the initial period of coating is increased andthen the accelerating voltage is lowered, thereby obtaining a coatedarticle with a diffraction intensity ratio of 15 or less and a halfvalue width of 0.8° or more. In general, if the thickness of a coatingfilm is less that 1 micron, the effect thereof is too small, while ifmore than 20 microns, peeling-off and embrittlement of the coating filmoften take place.

When the accelerating voltage is changed as described above, thediffraction intensity ratio and half value width are correspondinglychanged, but the quantity or degree of changes depends upon the variety,shape and dimension of a substrate, the interior dimension or mechanismof an ion plating apparatus and the ionization efficiency. In addition,it differs depending on materials to be vapor deposited, for example,whether it is titanium carbide or titanium nitride, and accordingly, itis difficult to determine unconditionally the diffraction intensityratio and half value width correspondingly to the accelerating voltage.In the case of coating titanium nitride by the use of titanium as amaterial to be vapor deposited and nitrogen as a reactive gas, however,the prior art method is carried out by applying an accelerating voltageof 0 to 2 KV throughout the coating and heating a substrate at atemperature of 500° to 700° C. to give a diffraction intensity ratio(I/Imax) magnified 100 times of 25 to 80 and half value width (2θ) of0.1° to 0.5°, while in the present invention, the accelerating voltageis preferably adjusted to 0.5 to 5 KV at the initial stage and loweredto 0.1 to 0.5 KV after the passage of about 5 to 10 minutes to give adiffraction intensity ratio of less than 15 and half value width of morethan 0.8°.

In an example according to the present invention, an end mill (10 mmφ)of high-speed steel (JIS SKH 55 equivalent to AISI M35) is coated withTiN with a thickness of 2.3 μm by holding an accelerating voltage of 0.5KV at the initial period and lowering to 0.2 KV after the passage of 5minutes, the coating being carried out over 25 minutes. The results ofX-ray diffraction show that the diffraction intensity ratio of the peakfrom the {220} plane and the secondly strong peak from the {111} planeis 13 of the latter to 100 of the former.

In another example, a throw-away insert (Insert type: SNG 533) of cermetof TiCN-TaN-Mo₂ C-WC-Ni-Co type is coated with TiN with a thickness of 9μm by holding an accelerating voltage of 5 KV at the initial period andlowering to 0.5 KV after the passage of 5 minutes, the coating beingcarried out over 110 minutes. The results of X-ray diffraction show thatthe diffraction intensity ratio of the highest peak from the {220} planeand the secondly strong diffraction peak from the {220} plane is 1.3 ofthe latter to 100 of the former.

The coating film in the highly hard material coated article of thepresent invention can be of a multi-film or combined with a film ofalumina or silicon nitride.

One embodiment of coating by means of an ion plating apparatus used inthe present invention will now be illustrated by the FIGURE:

Substrate 5 is fitted to substrate holder 6 and vacuum chamber 1 isevacuated to a pressure of 8×10⁻³ Pa or less by means of evacuatingdevice 2. Argon gas is introduced into vacuum chamber 1 to a pressure ofabout 3 Pa from gas feed system 3. A negative voltage of about 1.5 KV isapplied to substrate 5 by substrate accelerating power supply 4 toproduce a glow discharge and to heat substrate 5, and the surface ofsubstrate 5 is thus cleaned. Feeding of the argon gas is stopped andvacuum chamber 1 is evacuated again.

Metal 13 of titanium, zirconium, hafnium or an alloy consisting of twoor more of these metals in water-cooled copper crucible 12 is irradiatedwith electron beam 11 emitted from electron gun 9 by operating powersource 10 for electron gun 9, melted and vaporized. A positive voltageof 20 to 100 V is applied to ionization electrode 7 by ionizationpowersource 8 and between ionization electrode 7 and molten metal 13 isproduced a discharge by secondary electrons emitted by bonbardment ofelectron beam 11 and molten metal 13 and the metallic vapor vaporizedfrom the surface of molten metal 13. At least one gas selected from thegroup consisting of nitrogen gas, acetylene gas and oxygen gas andmixtures thereof is introduced as a reactive gas into vacuum chamber 1from gas feed system 3 so as to give a pressure of 2.5×10⁻² to 9.5×10⁻²Pa. Substrate 5 is revolved be revolving mechanism 14, to which anegative voltage of 0.5 to 5 KV is applied by substrate acceleratingpower source 4. In this case, an accelerating voltage can be applied toaccelerating electrode 15 by accelerating power source 16 despiteapplication of a voltage to substrate 5. Shutter 17 is opened andcoating of substrate 5 is then started. After the passage of 5 to 10minutes, the accelerating voltage is lowered to a negative voltage of0.1 to 0.5 KV. If substrate 5 is on the earth or the lower potential andis accelerated by accelerating electrode 15, the substrate is notoverheated and thus it is not necessary to lower the acceleratingvoltage. In this way, a highly hard material coated article of thepresent invention is obtained.

The following examples are given in order to illustrate the presentinvention in detail without limiting the same.

EXAMPLES

Using the above described ion plating apparatus, a substrate (Inserttype: SPG 422) consisting of cemented carbide alloy P 30 was coatedunder various conditions as shown in the following table and subjectedto assessment (Table 1 and Table 2):

                                      TABLE 1                                     __________________________________________________________________________                            Initial Conditions                                                                         Stationary Conditions                       Evapo-                                                                             Ambient         Power                                                                             Power    Power                                                                             Power                                   ration                                                                             pressure                                                                             Ambient  Source                                                                            Source                                                                             Time                                                                              Source                                                                            Source                                                                             Time                            No.                                                                              Material                                                                           (× 10.sup.-2 pa)                                                               Gas      4 (KV)                                                                            16 (KV)                                                                            (min)                                                                             4 (KV)                                                                            16 (KV)                                                                            (min)                           __________________________________________________________________________    1  Non-coated Article   --  --   --  --  --   --                              2  Ti   4      N.sub.2 + C.sub.2 H.sub.2                                                              0.1 1.5  5   0.1 1.5  50                              3  Ti   4      N.sub.2 + C.sub.2 H.sub.2                                                              1.5 0    5   0.3 0    50                              4  By Prior Art PVD Process                                                   5  By Prior Art CVD Process                                                   6  Ti   4.5    N.sub.2  0.1 2.0  8   0.1 2.0  50                              7  Ti   4.5    N.sub.2  2.0 0    8   0.5 0    50                              8  By Prior Art PVD Process                                                   9  Ti   4      N.sub.2 +  C.sub.2 H.sub.2 + O.sub.2                                                   0.1 1.8  5   0.1 1.8  50                              10 Ti   4      N.sub.2 + C.sub.2 H.sub.2 + O.sub.2                                                    2.0 0    5   0.5 0    50                              11 By Prior Art PVD Process                                                   12 Zr   3      C.sub.2 H.sub.2                                                                        0.1 3.0  10  0.1 3.0  150                             13 Zr   3      C.sub.2 H.sub.2                                                                        1.8 0    10  0.6 0                                    14 By Prior Art PVD Process                                                   15 Hf   2.8    N.sub.2  0.1 3.5  10  0.1 3.5  200                             16 Hf   2.8    N.sub.2  3.0 0    10  0.6 0                                    17 By Prior Art PVD Process                                                   __________________________________________________________________________                         Secondly                                                                Strongest                                                                           Strong     (220 Plane Broken State After                            Film                                                                              Diffrac-                                                                            Diffrac-                                                                            Intensity                                                                          Diffraction Cutting Test                                 Thick-                                                                            tion Plane                                                                          tion Plane                                                                          Ratio                                                                              Peak Half                                     Film       ness                                                                              (Intensity                                                                          (Intensity                                                                          (I/Imax)                                                                           Value Width                                   Quality    (μm)                                                                           Imax) I)    × 100                                                                        (2θ)                                                                           (Flank Wear Width)                     __________________________________________________________________________    --         --  --    --    --   --     after 20 min 0.29 mm                   Ti(CN)     4.5 {220} {200} 5.7  1.6°                                                                          after 20 min 0.10 mm                   Ti(CN)     4.6 {220} {111} 8.3  1.2°                                                                          after 20 min 0.14 mm                   Ti(CN)     4.5 {220} {111} 71.3 0.3°                                                                          after 10 min peeling                   Ti(CN)     4.5 {220} {111} 29.7 0.3°                                                                          after 1 min broken                     TiN        4.6 {220} {111} 4.1  1.9°                                                                          after 20 min 0.12 mm                   TiN        4.8 {220} {111} 7.7  1.1°                                                                          after 20 min 0.15 mm                   TiN        4.5 {220} {111} 68.1 0.2°                                                                          after 7 min peeling                    Ti(CNO)    4.5 {220} {200} 5.3  1.8°                                                                          after 20 min 0.12 mm                   Ti(CNO)    4.5 {220} {200} 7.9  1.1°                                                                          after 20 min 0.14 mm                   Ti(CNO)    4.2 {200} {111} 59.9 0.3°                                                                          after 7 min peeling                    ZrC        3.9 {220} {200} 3.5  2.0°                                                                          after 20 min 0.09 mm                   ZrC        4.1 {220} {111} 8.0  1.5°                                                                          after 20 min 0.12 mm                   ZrC        4.3 {220} {111} 67.5 0.3°                                                                          after 3 min peeling                    HfN        2.2 {220} {200} 3.1  2.1°                                                                          after 20 min 0.13 mm                   HfN        2.4 {220} {111} 7.2  1.7°                                                                          after 20 min 0.16 mm                   HfN        2.0 {200} {111} 73.3 0.3°                                                                          after 4 min peeling                    __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                        Property Assessment Condition                                                 Item            Contents                                                      ______________________________________                                        Cutting Method  Face milling                                                  Workpiece                                                                     Material        SCM 3 (JIS)                                                   Hardness        Hs 32                                                         Dimension       width 100 mm: length 300 mm                                   Tool (cutter)   Milling cutter with one insert                                                (cutter diameter 160 mm)                                      Cutting Conditions                                                            Speed           180 m/min                                                     Cut             3 mm                                                          Feed            0.2 mm/rev                                                    ______________________________________                                    

The test results of the resulting samples show that the coated articlesof the present invention have much more excellent properties orperformances than the prior art coated articles and in comparison withthe non-coated article, wear resistance is 1.8 to 3.2 times moreexcellent. When the coated articles of the present invention arecompared with each other, samples whose X-ray diffraction intensityratio (I/Imax)×100 is small and half value width of {220} planediffraction peak is large have better performances.

EXAMPLE 2

Using the ion plating apparatus of Example 1, titanium was heated andevaporated by an electron beam, ionized at an ionizing potential of +40V and deposited on a hob with module 1 and 20° in pressure angle (JISSKH 57) at a substrate potential of -0.8 KV for 5 minutes and -0.5 KVfor 25 minutes in a mixed gas under a total pressure of 5×10⁻⁴ Torr, inwhich the partial pressure of acetylene was 2×10⁻⁴ Torr and the partialpressure of nitrogen was 3×10⁻⁴ Torr, thus obtaining a coated productwith an intensity ratio [(I₂₀₀ /I₂₂₀)×100] of 9.7 and a half value widthof 1.0° on 2θ scale. The thus treated hob was subjected to gear cuttingof JIS S50C workpiece at a cutting speed of 106 m/min and 1061 rpm inthe presence of cutting oil. 230 pieces could be machined. On the otherhand, when a conventional tool cut only 100 pieces, the tool lifeexpired.

In cutting tools, wear resisting tools, wear parts or decorationarticles coated with highly hard materials according to the presentinvention, a material for a part requiring at least a wear resistance,heat resistance and corrosion resistance is generally chosen fromcermets, cemented carbides, tool steels and stainless steels. Forexample, a throw-away insert of a cermet or cemented carbides coatedwith a highly hard material according to the present invention exhibitsexcellent performances, in particular, for milling operations.

What is claimed is:
 1. A highly hard material coated article whichcomprises a substrate of a tool or part thereof consisting of cermet,cemented carbide, tool steel or stainless steel and at least one highlyhard material coated thereon selected from the group consisting ofcarbides, nitrides and carbonitrides of at least one of titanium,zirconium and hafnium and solid solutions thereof and those in whichoxygen is dissolved, the crystals of the coated film being stronglyorientated in the direction of <220> for the surface of the tool or partthereof so that the diffraction intensity ratio of the peak from the{220} plane and the secondly strong diffraction peak in the X-raydiffraction using Cu-Kα ray, that is, the diffraction intensity ratio isat most 15 of the latter to 100 of the former, and the half value widthof the diffraction peak from the {220} plane of the coating film beingat least 0.8° on a 2θ scale, said coating being formed by ion platingthe substrate under conditions such that the accelerating voltage ishigh during the plating step for a short time in the initial stagesufficient to maintain said diffraction intensity ratio of the coatedfilm as above and then lowering voltage sufficient to maintain said halfvalue width to at least 0.8.
 2. The highly hard material coated articleof claim 1, in which the tool is a throw-away insert for milling, whichis of a cermet or cemented carbide.
 3. The highly hard material coatedarticle of claim 1, in which the tool is a gear cutter.
 4. The highlyhard material coated article of claim 1, in which the ion plating methodis carried out by holding an accelerating voltage of 0.5 to 5 KV at theinitial period and lowering it to 0.1 to 0.5 KV after the passage of 5to 10 minutes.